scholarly journals BEACH EROSION COUNTERMEASURE USING NEW ARTIFICIAL REEF BLOCKS

2012 ◽  
Vol 1 (33) ◽  
pp. 107 ◽  
Author(s):  
Kyuhan Kim ◽  
Sungwon Shin ◽  
Chongkun Pyun ◽  
Hyun Dong Kim ◽  
Nobuhisa Kobayashi
Keyword(s):  
Wave Breaking ◽  
Laboratory Experiments ◽  
Wave Attenuation ◽  
Three Dimensional ◽  
Artificial Reef ◽  
Beach Erosion ◽  
Return Flow ◽  
Two Dimensional ◽  
Flow Mechanism ◽  
Submerged Breakwater

Two-dimensional and three-dimensional laboratory experiments were conducted to investigate not only the flow mechanism near the submerged breakwater but the performance of two newly developed eco-friendly artificial reef blocks. The results of two-dimensional experiments proved that new artificial blocks (EREEB) showed a better performance than TTP in terms of wave attenuation due to wave breaking turbulence near the crest of the structure. Three-dimensional experiments convinced that installing another type of new artificial block (WERF) in between submerged breakwater reduced the return flow velocity more than 50% compared with the gap between the breakwaters is empty. Therefore, these two types of newly developed artificial reef block can contribute the counter measure of beach erosion and habitat of sea lives.

Erosion Mitigation Using Submerged Breakwater Composed of Artificial Reefs

2015 ◽  
Vol 744-746 ◽  
pp. 1171-1174
Author(s):  
Kyu Han Kim ◽  
Bum Shick Shin
Keyword(s):  
Wave Attenuation ◽  
Three Dimensional ◽  
Artificial Reef ◽  
Beach Erosion ◽  
Artificial Reefs ◽  
Return Flow ◽  
Two Dimensional ◽  
Submerged Breakwater ◽  
Erosion Mitigation ◽  
Study Offer

In this study, erosion mitigation by submerged breakwater with artificial reefs is investigated among other means of countermeasures. Beach erosion mechanism near the submerged breakwater and the performance of artificial reef blocks are analyzed in the laboratory. Two-dimensional and three-dimensional laboratory experiments are applied to the analysis. The results of two-dimensional experiments prove that new artifi-cial blocks showed a better performance than the existing blocks in terms of wave attenuation due to wave breaking turbulence near the crest of the structure. Three-dimensional experiments show reduced return flow velocity by half by installing another type of new artificial block in between submerged breakwaters. Return flow has been creating vulnerability in countermeasures by submerged breakwater. Therefore, artifi-cial reef blocks suggested by this study offer solutions to the existing mitigation problems with submerged breakwater.

scholarly journals The magnetorotational instability prefers three dimensions

2020 ◽  
Vol 476 (2233) ◽  
pp. 20190622
Author(s):  
Jeffrey S. Oishi ◽  
Geoffrey M. Vasil ◽  
Morgan Baxter ◽  
Andrew Swan ◽  
Keaton J. Burns ◽  
...  
Keyword(s):  
Shear Rate ◽  
Angular Velocity ◽  
Laboratory Experiments ◽  
Three Dimensional ◽  
Linear Instability ◽  
Three Dimensions ◽  
Two Dimensional ◽  
Magnetorotational Instability ◽  
Dynamo Action ◽  
Wide Range

The magnetorotational instability (MRI) occurs when a weak magnetic field destabilizes a rotating, electrically conducting fluid with inwardly increasing angular velocity. The MRI is essential to astrophysical disc theory where the shear is typically Keplerian. Internal shear layers in stars may also be MRI-unstable, and they take a wide range of profiles, including near-critical. We show that the fastest growing modes of an ideal magnetofluid are three-dimensional provided the shear rate, S , is near the two-dimensional onset value, S c . For a Keplerian shear, three-dimensional modes are unstable above S  ≈ 0.10 S c , and dominate the two-dimensional modes until S  ≈ 2.05 S c . These three-dimensional modes dominate for shear profiles relevant to stars and at magnetic Prandtl numbers relevant to liquid-metal laboratory experiments. Significant numbers of rapidly growing three-dimensional modes remainy well past 2.05 S c . These finding are significant in three ways. First, weakly nonlinear theory suggests that the MRI saturates by pushing the shear rate to its critical value. This can happen for systems, such as stars and laboratory experiments, that can rearrange their angular velocity profiles. Second, the non-normal character and large transient growth of MRI modes should be important whenever three-dimensionality exists. Finally, three-dimensional growth suggests direct dynamo action driven from the linear instability.

Azimuthal investigation of compressional seismic-wave attenuation in a fractured reservoir

Geophysics ◽  
2019 ◽  
Vol 84 (6) ◽  
pp. B437-B446 ◽  
Author(s):  
Fateh Bouchaala ◽  
Mohammed Y. Ali ◽  
Jun Matsushima ◽  
Youcef Bouzidi ◽  
Eric M. Takam Takougang ◽  
...  
Keyword(s):  
United Arab Emirates ◽  
Seismic Wave ◽  
Wave Attenuation ◽  
Three Dimensional ◽  
Fractured Reservoir ◽  
Flow Mechanism ◽  
Seismic Wave Attenuation ◽  
Seismic Profiling ◽  
Vertical Seismic Profiling ◽  
The Rose

Three-dimensional vertical seismic profiling data acquired from an oilfield located in Abu Dhabi, United Arab Emirates, were used to obtain a high-resolution multioffset azimuthal estimate of compressional seismic wave attenuation. On the basis of the assumption that the fracture strike corresponds to the azimuthal direction [Formula: see text] at which the attenuation is minimized, fracture orientations were obtained in three reservoir units. Two approaches were used to determine [Formula: see text]: first from the variation of the absolute attenuation [Formula: see text] with the azimuth and second from the variation of the relative attenuation [Formula: see text] with the azimuth. The rose diagrams of [Formula: see text] estimated from the [Formula: see text] variation indicated better agreement with those showing the strikes of open and cemented fractures obtained from core interpretation than with either of those showing the two types of fractures separately. However, the rose diagrams of [Formula: see text] estimated from the variation of [Formula: see text] were more similar to those showing the strikes of open fractures obtained from core and Fullbore Formation Microimager data. This observation can be explained by the fact that in the first approach, all types of fractures contribute to the scattering and fluid-related mechanisms of [Formula: see text]. However, in the second approach, [Formula: see text] is obtained from a least-squares fitting of the variation of [Formula: see text] with the azimuth, which is based on the squirt flow mechanism that is caused by the movement of fluid between grain pores and fractures. Therefore, a comparison of the orientations obtained using these two approaches can be an efficient way to separately determine the orientations of open and cemented fractures.

Direct numerical simulation of a breaking inertia–gravity wave

2013 ◽  
Vol 722 ◽  
pp. 424-436 ◽  
Author(s):  
S. Remmler ◽  
M. D. Fruman ◽  
S. Hickel
Keyword(s):  
Gravity Wave ◽  
Wave Breaking ◽  
Middle Atmosphere ◽  
Dimensional Space ◽  
Three Dimensional ◽  
Vertical Direction ◽  
Domain Size ◽  
Boussinesq Equations ◽  
Two Dimensional ◽  
Instability Modes

AbstractWe have performed fully resolved three-dimensional numerical simulations of a statically unstable monochromatic inertia–gravity wave using the Boussinesq equations on an $f$-plane with constant stratification. The chosen parameters represent a gravity wave with almost vertical direction of propagation and a wavelength of 3 km breaking in the middle atmosphere. We initialized the simulation with a statically unstable gravity wave perturbed by its leading transverse normal mode and the leading instability modes of the time-dependent wave breaking in a two-dimensional space. The wave was simulated for approximately 16 h, which is twice the wave period. After the first breaking triggered by the imposed perturbation, two secondary breaking events are observed. Similarities and differences between the three-dimensional and previous two-dimensional solutions of the problem and effects of domain size and initial perturbations are discussed.

On the measurement of the turbulent diffusivity of a large-scale magnetic field

2013 ◽  
Vol 717 ◽  
pp. 347-360 ◽  
Author(s):  
S. M. Tobias ◽  
F. Cattaneo
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Laboratory Experiments ◽  
Three Dimensional ◽  
Effective Diffusivity ◽  
Dimensional System ◽  
Two Dimensional ◽  
Electrically Conducting ◽  
State Response ◽  
Large Scale Magnetic Field

AbstractWe argue that a method developed by Ångström (Ann. Phys. Chem., vol. 114, 1861, pp. 513–530) to measure the thermal conductivity of solids can be adapted to determine the effective diffusivity of a large-scale magnetic field in a turbulent electrically conducting fluid. The method consists of applying an oscillatory source and measuring the steady-state response. We illustrate this method in a two-dimensional system. This geometry is chosen because it is possible to compare the results with independent methods that are restricted to two-dimensional flows. We describe two variants of this method: one (the ‘turbulent Ångström method’) that is better suited to laboratory experiments and a second (the ‘method of oscillatory sines’) that is effective for numerical experiments. We show that, if correctly implemented, all methods agree. Based on these results we argue that these methods can be extended to three-dimensional numerical simulations and laboratory experiments.

scholarly journals A THEORETICAL AND EXPERIMENTAL STUDY OF UNDERTOW

1984 ◽  
Vol 1 (19) ◽  
pp. 151 ◽  
Author(s):  
J. Buhr Hansen ◽  
I.A. Svendsen
Keyword(s):  
Experimental Study ◽  
Mass Flux ◽  
Laboratory Experiments ◽  
Three Dimensional ◽  
Two Dimensional ◽  
Rip Currents ◽  
Longshore Currents ◽  
Theoretical Results ◽  
Recent Laboratory

It is well known that on a three-dimensional beach large volumes of water carried shorewards by the breakers feed longshore currents, which eventually escape back through the breaker line, often as rip currents. In a steady two-dimensional situation, however, the mass flux represented by (among other things) the surface roller in the breakers returns as a seaward current close to the bottom. This current is called the undertow. In this paper theoretical results for the undertow are compared with the results of recent laboratory experiments.

Instability and focusing of internal tides in the deep ocean

2007 ◽  
Vol 588 ◽  
pp. 1-28 ◽  
Author(s):  
OLIVER BÜHLER ◽  
CAROLINE J. MULLER
Keyword(s):  
Ocean Circulation ◽  
Wave Breaking ◽  
Large Scale ◽  
Three Dimensional ◽  
Deep Ocean ◽  
Internal Gravity Waves ◽  
Internal Tides ◽  
Unstable Wave ◽  
Two Dimensional ◽  
Sea Floor

The interaction of tidal currents with sea-floor topography results in the radiation of internal gravity waves into the ocean interior. These waves are called internal tides and their dissipation due to nonlinear wave breaking and concomitant three-dimensional turbulence could play an important role in the mixing of the abyssal ocean, and hence in controlling the large-scale ocean circulation.As part of on-going work aimed at providing a theory for the vertical distribution of wave breaking over sea-floor topography, in this paper we investigate the instability of internal tides in a very simple linear model that helps us to relate the formation of unstable regions to simple features in the sea-floor topography. For two-dimensional tides over one-dimensional topography we find that the formation of overturning instabilities is closely linked to the singularities in the topography shape and that it is possible to have stable waves at the sea floor and unstable waves in the ocean interior above.For three-dimensional tides over two-dimensional topography there is in addition an effect of geometric focusing of wave energy into localized regions of high wave amplitude, and we investigate this focusing effect in simple examples. Overall, we find that the distribution of unstable wave breaking regions can be highly non-uniform even for very simple idealized topography shapes.

scholarly journals Plane and Surface Acoustic Waves Manipulation by Three-Dimensional Composite Phononic Pillars with 3D Bandgap and Defect Analysis

Acoustics ◽  
2021 ◽  
Vol 3 (1) ◽  
pp. 25-41
Author(s):  
Muhammad ◽  
C.W. Lim ◽  
Andrew Y. T. Leung
Keyword(s):  
Acoustic Waves ◽  
Wave Attenuation ◽  
Numerical Technique ◽  
Surface Acoustic Waves ◽  
Three Dimensional ◽  
Phononic Crystals ◽  
Defect State ◽  
Two Dimensional ◽  
Defect Analysis ◽  
Acoustic Metamaterials

The current century witnessed an overwhelming research interest in phononic crystals (PnCs) and acoustic metamaterials (AMs) research owing to their fantastic properties in manipulating acoustic and elastic waves that are inconceivable from naturally occurring materials. Extensive research literature about the dynamical and mechanical properties of acoustic metamaterials currently exists, and this maturing research field is now finding possible industrial and infrastructural applications. The present study proposes a novel 3D composite multilayered phononic pillars capable of inducing two-dimensional and three-dimensional complete bandgaps (BGs). A phononic structure that consisted of silicon and tungsten layers was subjected to both plane and surface acoustic waves in three-dimensional and two-dimensional periodic systems, respectively. By frequency response study, the wave attenuation, trapping/localization, transmission, and defect analysis was carried out for both plane and surface acoustic waves. In the bandgap, the localized defect state was studied for both plane and surface acoustic waves separately. At the defect state, the localization of both plane and surface acoustic waves was observed. By varying the defect size, the localized frequency can be made tailorable. The study is based on a numerical technique, and it is validated by comparison with a reported theoretical work. The findings may provide a new perspective and insight for the designs and applications of three-dimensional phononic crystals for surface acoustic wave and plane wave manipulation, particularly for energy harvesting, sensing, focusing and waves isolation/attenuation purposes.

Spontaneous breaking of reflexional symmetry in real quasi-two-dimensional turbulence: stochastic travelling waves and helical solitons in atmosphere and laboratory

1993 ◽  
Vol 441 (1911) ◽  
pp. 147-155 ◽  
Keyword(s):  
Experimental Data ◽  
Boundary Layer ◽  
Laboratory Experiments ◽  
Travelling Waves ◽  
Qualitative Difference ◽  
Three Dimensional ◽  
Spontaneous Breaking ◽  
Two Dimensional ◽  
Boundary Layer Turbulence ◽  
The Difference

The theme of this note is the qualitative difference between strictly two-dimensional (2D) and quasi-two-dimensional (Q2D) turbulence in spite of the ‘smallness’ of the difference in their geometry. It is argued that the Q2D régime arises as a result of a spontaneous breaking of reflexional symmetry, which in turn is a consequence of the instability of 2D turbulence to three-dimensional helical travelling waves and solitons (through super-critical and sub-critical bifurcations). The difference between 2D and Q2D turbulence, which is primarily of a topological nature (related to helicity and super helicity) is manifested in different spectral and diffusive properties. The arguments are supported by a large number of experimental data from laboratory experiments (stably stratified, rotating, magnetohydrodynamic and boundary layer turbulence) and from observations in the stratosphere.

scholarly journals LONG TERM PERFORMANCE OF A SUBMERGED COASTAL CONTROL STRUCTURE: A CASE STUDY OF THE NARROWNECK MULTI-FUNCTIONAL ARTIFICIAL REEF

2012 ◽  
Vol 1 (33) ◽  
pp. 54 ◽  
Author(s):  
Angus Jackson ◽  
Rodger Tomlinson ◽  
Bobbie Corbett ◽  
Darrell Strauss
Keyword(s):  
Large Scale ◽  
Control Point ◽  
Artificial Reef ◽  
Beach Erosion ◽  
Gold Coast ◽  
Storm Events ◽  
Marine Habitat ◽  
Submerged Breakwater ◽  
Long Term Performance ◽  
Term Performance

In response to the increasing occurrences of beach erosion along Surfers Paradise and Main Beaches - Gold Coast, Australia, the Northern Gold Coast Beach Protection Strategy [NGCBPS] was developed to widen the beach by 20-30m as well as improving surfing conditions as a secondary objective. The strategy, implemented in 1999- 2000, involved large-scale beach nourishment and construction of a submerged breakwater “reef” to act as a control point at Narrowneck. Construction of the reef involved innovative filling and placement methods using very large sand filled geotextile containers coupled with significant advances with regards to design of the geotextile material and containers. In the 11 years since construction, there has been substantial monitoring of the project since its completion in late 2000 including: - video imaging using webcams; hydrographic and beach surveys; aerial and oblique photography; surf and surf safety observations and GPS surfing track plots; and geotextile container condition and stability. This paper presents an update on the performance of the reef over the last four years. In particular, the response of the structure and the shoreline to a series of major storm events in 2009 has been examined. The results have shown that the erosion caused by these major events was accommodated within the wider beach created in 1999. Over the next 2 years there was a gradual recovery in the lee of the reef with a subtle groyne effect resulting in an even larger increase in the width of the updrift beach. A detailed underwater condition survey was also undertaken in 2011, to determine changes in the condition of the geotextile containers. This revealed a number of containers missing or damaged, and that seaward containers were covered by sand. The marine habitat which has been a feature of the reef has been impacted by the increased coverage of sand, but still shows high abundance and biodiversity.

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